The present invention relates to motor drives providing synthesized power waveforms to electric motors to control the operation of the motors, and in particular to an improved, modular interconnection system for such motor drives.
Industrial controllers use specialized computers and other electronic circuitry to control industrial processes and machines. The elements of an industrial controller must be easily reconfigured so that the industrial controller may be easily adapted to a variety of applications. For this reason, the elements of an industrial controller are normally modular, allowing different modules to be selected and assembled within a rack that provides for an interconnection between the modules. This approach allows a wide variety of different hardware configurations to be created rapidly.
Motor drives differ from a standard industrial controller in that extremely high communication rates are required among the different drive controls, for example, to precisely synchronize inverter/rectifier control in real time. Gating signals to rectifiers or inverters requires low latency. For this reason, the modules of a motor drive are normally interconnected with dedicated parallel communication channels between the various drive modules. Parallel communication channels communicate the bits of multi-bit data simultaneously with each bit assigned to a different conductor. Single bits of data, for example gating signals, may be assigned to a unique conductor so that multiple single bits are also transmitted in parallel. In this way, extremely high speeds of data transfer or low latency may be reached. These parallel communication channels may be implemented on a backplane, typically a printed circuit having multiple parallel conductors joining multiple connectors that may attach to the modules. As with an industrial controller, the modules may be assembled together within a rack abutting the backplane.
In an alternative to the backplane configuration, dedicated parallel communication channels may be implemented by the use of pairs of electrical connectors joined by ribbon cables or the like providing for the parallel conductors. The use of separate parallel channels can increase data speeds and reduce latency.
A drawback to such parallel bus structures is that they are relatively inflexible. In the backplane system, when additional single bit data must be transmitted, new conductors must be added to the backplane. This may require a fundamental redesign of the circuit boards of the system or may be impractical for reasons of costs or equipment size limitations. In the harness system, even though new wires may be added to the harness, the connector sizes must change requiring a change of the module circuit boards. Making and changing the connections between modules in the harness system is difficult, requiring the physical routing of wires between particular boards.